A few extra degrees — or minutes — can erase carotenoids and spike peroxide values in palm oil. Trials show that dialing down temperature and time, from clarification to deodorization, preserves quality without sacrificing separation.
Palm oil’s quality is written in its thermal history. High temperatures accelerate hydrolytic and oxidative reactions — raising free fatty acids (FFA) and peroxide value (PV) — and strip out pigments and nutrients like β‑carotene and tocopherols. In one experiment, crude palm oil exposed to 120 °C lost nearly all carotenoids in a few hours: β‑carotene fell from 2.34 to 0.33 mg/g after 7.5 hours at 120 °C (link.springer.com). Even palm olein held at 80–120 °C is stable for only about two hours; beyond that, oxidation products and FFA accumulate markedly (jopr.mpob.gov.my).
Process engineers talk in kinetics: reaction rates roughly double with every +10 °C rise. In palm oil, prolonged heat drives linear increases in PV and FFA, with oil deterioration observed after about two hours under moderate heating (80–120 °C) (jopr.mpob.gov.my). The practical takeaway is unambiguous: minimize cumulative time above 100 °C to preserve quality.
Thermal sensitivity and nutrient losses
Color and nutrients fade with heat. Trials show carotene content drops steadily with rising temperature and time; for example, 516 ppm carotene was retained after 1.5 hours at 55–60 °C, with much lower retention at higher settings (researchgate.net) (researchgate.net). Empirical models for red palm oil report carotene retention of about –7.8·ln(time)+91.0 and –764·ln(T)+4693; doubling time from 1 to 2 hours at ~140 °C cuts carotene retention by ≈6% (online-journal.unja.ac.id).
Clarification temperatures and residence time
Clarification (separating oil from water, mud, and solids) is traditionally run hot (≈80–90 °C) to reduce viscosity. But Indonesian trials found that raising clarification temperature and duration sharply increases PV while lowering carotene (researchgate.net). Operating at a moderate 55–60 °C for 1.5 hours yielded crude palm oil with PV 3.15 meq/kg and carotene at 516 ppm (researchgate.net). In summary, ↑T or ↑time ⇒ ↑PV, ↓carotene, ↓dirt content (researchgate.net) (researchgate.net).
Where tanks are used, traditional settling systems (clarifiers) can be paired with tighter temperature setpoints to manage hold times (clarifier). The operational goal is simple: sufficient viscosity reduction for separation, with the lowest viable temperature and shortest possible residence time.
Mechanical separation and dilution cuts
Modern mechanical separation helps keep the heat off. Two‑phase decanter systems, for example, operate with minimal or no water injection — saving up to 90% of dilution water — so the oil need not be overheated to separate (gea.com). The oil exits nearly at its extraction temperature, limiting heating time. These systems “ensure the best possible oil quality” by retaining natural constituents (analogous to polyphenols in olive oil) since minimal water contact prevents hydrolysis (gea.com).
In practice, mills can adopt continuous decanters with heated oil feed and short residence (1–2 hours) to achieve >2.1% solids oxide levels (per [9]) without extended heating. Studies also report up to 83% reduction in effluent by replacing conventional tanks with decanters+evaporation .
Degumming and neutralization controls
In refining (“purification”), degumming (acid treatment converting gums to hydratable form) and caustic neutralization typically occur at ~70–90 °C. In chemical refining, crude oil is first treated with phosphoric acid then neutralized with caustic soda at about 80–85 °C (mdpi.com) (mdpi.com). Metered addition is standard practice in such steps, using equipment such as dosing pumps to sequence the reagents.
Recent optimization studies found optimal acid‑degumming at 90 °C for ~30 minutes (with 0.06% H₃PO₄), which removed phosphorus and hydroperoxides effectively while minimizing harmful process contaminants — glycidyl esters (GE) and 3‑MCPD esters (3‑MCPDE) (mdpi.com) (mdpi.com). Under those conditions, final RBD oil (refined, bleached, deodorized) recorded ~0.61 mg/kg GE and ~0.59 mg/kg 3‑MCPDE — near or below industry limits (mdpi.com). After degumming, caustic neutralization also occurs around 80–85 °C and is timed in minutes to avoid excessive saponification; spent soap is removed quickly. Keeping degumming/neutralization short (<1 hour total) and at ≤90 °C prevents undue oil degradation; monitoring residual phosphorus and FFA ensures reactions are complete without overexposure.
Bleaching under vacuum
Bleaching mixes oil with adsorbent clay (bleaching earth) under vacuum to remove pigments and trace metals. Typical conditions are 90–130 °C for 15–40 minutes at 50–125 mmHg. The vacuum both lowers the needed temperature and prevents oxidation. Most mills run ~105–110 °C for only 20–30 minutes under vacuum; longer contact broadens color removal but risks oil darkening if adsorbents saturate (cnhuataigroup.com). The target is Lovibond color and redox metrics achieved with minimal thermal load.
Deodorization severity and tradeoffs
Deodorization — vacuum steam stripping of volatiles and FFA — is the hottest step, typically 200–260 °C. Standard operations use ~230–250 °C at 2–6 mbar for ~30–90 minutes (often ≈1 hour). These conditions eliminate >99.9% FFA (down to ~0.1%) and destroy peroxides and odors — but they also destroy carotenoids and can generate 3‑MCPD and glycidyl esters if chloride or DAG are present.
Countermeasures include highly efficient vacuum (a few mbar), high‑velocity fine steam, and shortened cycles (e.g., short‑path designs). Data show a tradeoff: at ~141 °C, about 2.35 hours of vacuum steam produced red palm oil with acceptable FFA (0.11%) and carotene (444 ppm) (online-journal.unja.ac.id), whereas a typical high‑temperature deodorization (~240 °C) would strip essentially all carotene. In practice, once residue specifications (FFA, Lovibond color) are met, the process should end.
Lower‑temperature deodorization (RPO example)
An Indonesian trial varied deodorization temperature (135–145 °C) and time (1–4 hours) at 20 mmHg and derived equations showing carotene retention falls ~7.8% per doubling of time and ≈ –764·ln(T)+4693 (online-journal.unja.ac.id). The optimal run (141.3 °C, 2.35 hours) yielded FFA 0.11%, PV 0.12 meq/kg, and carotene 444 ppm — meeting SNI specs (≥400 ppm carotene, FFA ~0.1%) (online-journal.unja.ac.id).
Process integration and time minimization
Clarifier setpoints: Rather than defaulting to 80–90 °C, use the lowest viable temperature for separation. Trials indicate 55–60 °C yields significantly better quality (researchgate.net). Mechanical separators — continuous decanters or three‑phase centrifuges — can achieve clear oil quickly without extensive heating. Minimizing water dilution (or using counterflow cooling water) shortens settling time.
Heat integration: Preheat only as needed and rapidly. Use heat exchangers to reach process temperature quickly, then remove heat immediately after the step. After clarification/centrifugation, route oil through a cooler or back to storage promptly to avoid extended holding at elevated temperature.
Separation technology: Two‑phase decanters (little/no dilution water) drastically cut the need for hot‑water settling (gea.com). In practice, decanting at ~60–70 °C can complete in under an hour if properly adjusted, versus several hours in a tank.
Downstream steps: Degumming/neutralization at 80–90 °C with total contact ~30–45 minutes, using efficient mixers and real‑time checks on FFA and residual phosphorus (mdpi.com). Bleaching under vacuum with high‑grade earth targets 15–30 minutes at ~100–110 °C (cnhuataigroup.com). Deodorization with high vacuum and steam aims for ~0.1% FFA in the shortest feasible time; some olein producers accept FFA ~0.15–0.2% to reduce cycle time.
Monitoring and standards: Rapid assays — inline PV and FFA sensors, colorimetric carotene tests — enable ending heating as soon as targets are reached. Standards (e.g., SNI and international) typically require CPO FFA <5%, RBD oil FFA ~0.1%, PV <10 meq/kg, and carotene >0.05% for CPO. Processes should meet, but not excessively surpass, these limits; for example, if mixing design or vacuum reaches FFA=0.1% 15% faster, operations can shorten holds accordingly.
Bottom line on temperature control
Precise temperature control and minimized high‑temperature dwell are crucial. Quantitative results show that even a few extra degrees or minutes significantly degrade quality (e.g., peroxide value doubles with excessive heat). Combining lower clarification temperatures, fast mechanical separations (centrifuges), and optimized refining (vacuum, shorter times) preserves antioxidants and holds FFA in check. For example, adopting a 60 °C clarifier and a 90 °C, 30‑minute degumming — instead of 85 °C and 120 °C — kept PV ≈3 meq/kg and carotene ≈500 ppm (researchgate.net) (mdpi.com). The data‑backed adjustments deliver high yield, compliance with Indonesian and international specifications, and better nutritional retention — with less heat.
Sources: Recent industry and academic studies (2018–2023) provide the data above (researchgate.net) (researchgate.net) (mdpi.com) (mdpi.com) (online-journal.unja.ac.id) (online-journal.unja.ac.id) (cnhuataigroup.com) (jopr.mpob.gov.my) (link.springer.com) (gea.com).
